Method and apparatus for cleaning substrates using liquid carbon dioxide

ABSTRACT

Methods for cleaning a microelectronic substrate in a cluster tool are described that include placing the substrate in a pressure chamber of a module in a cluster tool; pressurizing the pressure chamber; introducing liquid CO 2  into the pressure chamber; cleaning the substrate in the pressure chamber; removing the liquid CO 2  from the pressure chamber, depressurizing the pressure chamber, and removing the substrate from the pressure chamber. Apparatus for processing a microelectronic substrate are also disclosed that that include a transfer module, a first processing module that employs liquid carbon dioxide as a cleaning fluid coupled to the transfer module, a second processing module coupled to the transfer module, and a transfer mechanism coupled to the transfer module. The transfer mechanism is configured to move the substrate between the first processing module and the second processing module.

FIELD OF THE INVENTION

[0001] The present invention relates to methods and apparatus for cleaning substrates, and, more particularly, to methods and apparatus for cleaning substrates using CO₂.

BACKGROUND OF THE INVENTION

[0002] Integrated circuits (ICs), optoelectronic devices, micromechanical devices and other precision fabrications are commonly formed using thin films applied to substrates. As part of the fabrication process, it is often necessary to remove or clean a portion or all of the thin film from the substrate. For example, in the manufacture of semiconductor wafers including ICs, a thin photoresist layer may be applied to the semiconductor substrate and subsequently removed.

[0003] Contaminants removed from surface features of microelectronic substrates after various manufacturing steps (e.g., after post-ion implant, ‘back end of the line’ (BEOL) cleans, ‘front end of the line’ (FEOL) cleans, and post chemical mechanical planarization (CMP) steps) may vary dramatically in nature and composition. Accordingly, cleaning and treating steps must address these contaminants with the appropriate chemistries and solvents to either react with, ionize, dissolve, swell, disperse, emulsify, or vaporize them from the substrate. As such, a variety of wet (e.g., water and solvent) cleaning processes, and dry (e.g., plasma) cleaning processes have been developed to address the broad variety of waste materials.

SUMMARY OF THE INVENTION

[0004] The present invention relates generally to, inter alia, the cleaning or treating of microelectronic substrates (such as semiconductor substrates) during or subsequent to the manufacturing of microelectronic substrates such as integrated circuits, microelectronic devices, MEM's, MEOM's and opto-electronic devices. Removal of surface contaminants and particulates is a key step in the integrated circuit fabrication process. There are numerous cleaning steps in the fabrication process including, but not limited to, pre-diffusion cleans, post-ash cleans, post-etch cleans, pre-metal deposition cleans, plasma strip, clean/strip, post-ion implantation cleans and post-chemical mechanical planarization (CMP) cleans. There are many types and sources of particulates and contaminants in the fabrication process. The particles and contaminants may be molecular, ionic, atomic or gaseous in nature. The source may be inherent (e.g., redeposition of resist) or extrinsic to the process (e.g., wafer transport).

[0005] In embodiments of the present invention, methods for cleaning a microelectronic substrate in a cluster tool that include placing the substrate in a pressure chamber of a module in a cluster tool, pressurizing the pressure chamber, introducing liquid CO₂ into the pressure chamber, cleaning the substrate in the pressure chamber, removing the liquid CO₂ from the pressure chamber, depressurizing the pressure chamber, and removing the substrate from the pressure chamber are provided.

[0006] In other embodiments of the present invention, apparatus for processing a microelectronic substrate are provided that include a transfer module, a first processing module that employs liquid carbon dioxide as a cleaning fluid coupled to the transfer module, and a transfer mechanism coupled to the transfer module. The transfer mechanism is configured to move the substrate between the first processing module and the second processing module.

[0007] The shift from Al/SiO₂ interconnect systems to Cu/low-k interconnect systems presents new challenges that may be effectively addressed using the methods and apparatus of the present invention. For example, a primary problem with the transition to Cu is the tendency of Cu to corrode when exposed to an oxidizing environment because Cu does not have the self-passivating properties of Al. Corrosion of Cu during cleans of dual damascene structures can result in high contact resistance, undercutting and lift-off of the dielectric layers, thereby reducing circuit yields. Additional concerns have focused on the chemical compatibility of traditional cleans with low-k materials. As an example, it has been demonstrated that amine chemistries gas from OSG and other inorganic spin-on dielectric films, causing via poisoning. Aspects of the present invention may address the currently challenging cleans of these new interconnect systems.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 illustrates a method of cleaning a substrate in a pressure chamber;

[0009]FIG. 2 illustrates a cluster tool according to embodiments of the present invention for performing fabrication, specifically chemical mechanical planarization, of a semiconductor substrate;

[0010]FIG. 3 illustrates a schematic representation of a cleaning apparatus according to embodiments of the present invention; and

[0011]FIG. 4 illustrates an embodiment of a cleaning apparatus according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention now is described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

[0013] It will be appreciated by those of skill in the art from the description herein that various components and steps as described herein below may be omitted or replaced with other (for example, conventional) components or steps as appropriate.

[0014] As used herein, the term “microelectronic substrate” should be interpreted broadly to include semiconductor substrates, semiconductor substrates on which one or more layer resides, integrated circuits, microelectronic workpieces, microelectronic devices, MEM's, MEOM's and opto-electronic devices.

[0015] As used herein, the term “processing time” means the time elapsed during a given process. For a process module, the process time is measured from the time a microelectronic substrate completely crosses the threshold of the process module (e.g., the module's pressure chamber) when placed into the module until the time the microelectronic substrate completely crosses the threshold of the process module when removed from the module.

[0016] Referring now to FIG. 1, a process for cleaning a microelectronic substrate in a cluster tool according to embodiments of the present invention will now be described. The microelectronic substrate is placed in a pressure chamber of a cleaning module of a cluster tool and the pressure chamber is sealed (110). Preferably, the pressure chamber is sealed utilizing a sealing controller located on the cluster tool as will be understood by those skilled in the art.

[0017] The pressure chamber is then pressurized (120). The pressure chamber is preferably pressurized utilizing carbon dioxide gas; however, it is to be understood that gases including, but not limited to, carbon dioxide, air, nitrogen, argon, helium, and mixtures thereof may be used to pressurize the pressure chamber. The pressure chamber is preferably pressurized to a pressure such that the temperature and pressure of the pressure chamber are within the liquid portion of a carbon dioxide phase diagram as will be understood by those skilled in the art. More preferably, the pressure chamber is pressurized to a pressure such that at a temperature of about 0 to 30° C., liquid CO₂ in the pressure chamber would be at saturation conditions or slightly (e.g., 1, 2, 3, 4 or 5° C.) subcooled.

[0018] Liquid CO₂ is then introduced into the pressure chamber (130). In some embodiments of methods of the present invention, the pressure chamber is partially filled with liquid CO₂ such that a liquid volume and a vapor volume are formed. In other embodiments, the introduction of the liquid CO₂ into the pressure chamber includes forming a pool of liquid CO₂ in the pressure chamber, and forming a gas phase in the pressure chamber that contacts the liquid CO₂ pool and separates the liquid CO₂ pool from a portion of the pressure chamber wall. The atmosphere may include CO₂ gas, a non-CO₂ gas, or a mixture thereof. Non-CO₂ gases include, but are not limited to, nitrogen, helium, argon, air, and mixtures thereof. The non-CO₂ gas is preferably an inert gas.

[0019] The temperature of the liquid CO₂ in the pressure chamber is maintained between about −57° C. and 31° C. Preferably, the temperature of the liquid CO₂ in the pressure chamber is maintained between about −5, 0 or 5° C. and 20, 25 or 30° C. More preferably, the temperature of the liquid CO₂ in the pressure chamber is maintained between about 5, 10 or15° C. and 20, 25 or 30° C.

[0020] During the introduction of liquid CO₂ into the chamber and/or during the subsequent cleaning process, the temperature in the pressure chamber is maintained at or below the critical temperature of CO₂ to ensure that the fluid remains in a liquid state. The pressure may be allowed to exceed the critical pressure of CO₂, provided the temperature is below the critical pressure. When the liquid CO₂ partially fills the pressure chamber such that a liquid CO₂ pool and a gas phase above the liquid CO₂ pool are formed in the pressure chamber, the temperature and optionally the pressure in the pressure chamber may be maintained below critical points by various means as will be understood by those skilled in the art. The temperature of the liquid CO₂ is preferably maintained below the critical temperature by cooling the liquid CO₂. While the liquid CO₂ may be cooled in situ (i.e., within the pressure chamber), the liquid CO₂ is preferably cooled by removing a portion of the liquid CO₂ from the pressure chamber, cooling the portion to a desired temperature below the critical temperature of liquid CO₂ or of the liquid CO₂ mixture if a secondary gas or cleaning adjuncts are used, and returning the portion of the liquid CO₂ to the pressure chamber.

[0021] In another embodiment in which a liquid and gas phase co-exist in the chamber, the partial pressure of CO₂ gas in the gas-phase of the pressure chamber is maintained below the saturation pressure of pure CO₂ at the temperature of the liquid CO₂ pool. The differential between the partial pressure of CO₂ gas in the gas-phase and the saturation pressure of pure CO₂ at the temperature of the liquid CO₂ pool is preferably between about 0.1 atmospheres and 10 atmospheres. The partial pressure of the CO₂ gas in the gas phase of the pressure chamber may be maintained below the saturation pressure corresponding to pure CO₂ at a given temperature by various means. For example, a secondary gas with a higher saturated vapor pressure than CO₂ can be used. Furthermore, when a secondary gas is used, the temperature of the liquid phase can be lowered and raised to adjust the partial pressure of the CO₂ in the gas phase. The various methods of maintaining the temperature and partial-pressure of CO₂ in the pressure chamber below saturation conditions for pure CO₂ may be used alone or may be used in combination.

[0022] In some embodiments of methods of the present invention, an adjunct is introduced into the pressure chamber. The adjunct is preferably introduced in an amount sufficient to facilitate cleaning or other processing of the substrate. As will be understood by those skilled in the art, the adjunct may be selected from various adjuncts including, but not limited to, water, oxidizers such as peroxides or permanganates, acids such as hydrofluoric, sulfuric, and nitric acid, bases such as secondary and tertiary amines, ammonium hydroxide, solvents such as organic carbonates, lactones, ketones, ethers, alcohols, sulfoxides, thiols, and alkanes, surfactants such as block copolymers or random copolymers composed of fluorinated segments and hydrophilic or lipophilic segments, surfactants with siloxane-based components and hydrophilic or lipophilic components, conventional ionic, and non-ionic hydrocarbon-based surfactants, salts such as ammonium fluoride and choline, and mixtures thereof. The process of introducing the adjunct into the pressure chamber may be performed before, concurrently with, and/or after the introduction of the liquid CO₂ into the pressure chamber. It may be preferable to introduce the liquid CO₂ and the adjunct into the pressure chamber as a mixture.

[0023] After the liquid CO₂ and the adjunct have been introduced into the pressure chamber, the adjunct may become admixed with the liquid CO₂. The density of the liquid CO₂ in the pressure chamber is preferably decreased to deposit the adjunct from the mixture onto the substrate. The density of the liquid CO₂ may be decreased in various ways. For example, the temperature of the liquid CO₂ in the pressure chamber may be increased and/or the pressure of fluid in the pressure chamber may be decreased. While embodiments of the present invention are described herein as utilizing liquid CO₂, it is to be understood that liquid compositions comprising liquid CO₂ could be used in the methods and/or apparatus of the present invention.

[0024] The substrate is cleaned using the liquid CO₂ (140). The substrate may be cleaned in various ways using the liquid CO₂ including, but not limited to, spraying the substrate with the liquid CO₂, immersing the substrate in the liquid CO₂, and flowing the liquid CO₂ across the surface of the substrate. It is to be understood that the process of cleaning the substrate using the liquid CO₂ may occur, either in part or in whole, during the process of introducing the liquid CO₂ into the pressure chamber. In preferred embodiments, a waste layer is on the microelectronic substrate, and the process of cleaning the substrate includes removing the waste layer from the substrate. The waste layer may be various waste layers that accumulate on microelectronic substrates during the fabrication of such substrates and may include, but not be limited to, chemical mechanical polishing residues, post-ion implantation residues, reactive ion etch residues, post-ash residues, photoresists, or mixtures thereof. The waste layer preferably includes a particulate phase.

[0025] The liquid CO₂ is removed from the pressure chamber (150). The liquid CO₂ may be removed from the pressure chamber after the substrate is substantially cleaned or the liquid CO₂ may be removed from the pressure chamber before the substrate is substantially cleaned. If the liquid CO₂ is removed from the pressure chamber before the substrate is substantially cleaned, additional liquid CO₂ is preferably introduced into the pressure chamber as described above with reference to block 130. In this way, a plurality (e.g., 2, 3, 4, 5, 6 or more) of liquid CO₂ introduction and removal processes may be performed. Preferably, the liquid CO₂ introduction and removal processes are repeated as necessary to obtain the desired cleanliness of the microelectronic substrate.

[0026] The liquid CO₂ may be removed from the pressure chamber by various processes. For example, the liquid CO₂ may be gravity drained from the pressure chamber. When this process is employed, the liquid CO₂ is preferably gravity drained from the pressure chamber into a liquid carbon dioxide storage tank. Vapor communication is preferably provided between a vapor space in the pressure chamber and a vapor space in the liquid carbon dioxide storage tank.

[0027] Preferably, the liquid CO₂ is removed from the pressure chamber by introducing a pressurized gas into the pressure chamber, and forced plug flowing the liquid CO₂ out of the pressure chamber. The pressurized gas may comprise CO₂ gas, supercritical CO₂, or a non-CO₂ gas. The non-CO₂ gas may be an inert gas, such as helium, a non-inert gas, such as nitrogen, argon, or air. The pressurized gas may also be a mixture of a CO₂ gas and a non-CO₂ gas or a mixture of non-CO₂ gas. When the pressurized gas is CO₂ gas, the CO₂ gas is preferably at a pressure that is greater than the pressure of the fluid in the pressure chamber and is preferably at a temperature that is greater than the temperature of the fluid in the pressure chamber.

[0028] In some embodiments of methods according to the present invention, the temperature of the fluid in the pressure chamber is cooled to a temperature below saturation temperature for the given pressure, termed “subcooling”, while removing the liquid from the pressure chamber. In cases where liquid and gas coexist, rapid cooling of the liquid phase brings the system out of equilibrium causing the gas phase to become supersaturated for a period of time until the system reaches equilibrium. Subcooling the liquid during draining can be advantageous in the prevention of boiling during the draining step and can speed the removal of the liquid. In other embodiments, greater than about 99 percent of the mass of the liquid CO₂ is removed from the pressure chamber as liquid CO₂, and, preferably, greater than about 99.5 percent of the mass of the liquid CO₂ in the pressure chamber is removed from the pressure chamber as liquid CO₂.

[0029] When removing the liquid CO₂ from the pressure chamber, the flow rate of liquid CO₂ out of the pressure chamber is preferably greater than about 0.1 chamber volumes per second, is more preferably greater than about 1.0 chamber volume per second and is still more preferably greater than about 3.0 chamber volumes per second.

[0030] After removing the liquid CO₂ from the pressure chamber, the pressure chamber is depressurized (160). In some embodiments according to the present invention, CO₂ gas remains in the pressure chamber after the removing of the liquid CO₂ from the pressure chamber. The depressurizing of the pressure chamber includes removing the CO₂ gas from the pressure chamber. The removed CO₂ gas is preferably conserved. For example, the removed CO₂ gas may be stored in a gas storage tank. The stored CO₂ gas may then be charged into the pressure chamber in a subsequent cleaning cycle. As another example, the removed CO₂ gas is transferred to another pressure chamber. The other pressure chamber is preferably in a module on a cluster tool. Preferably, the cluster tool is the same cluster tool as the one containing the cleaning module. As still another example, the CO₂ gas is removed from the pressure chamber, stored in a gas storage tank, and transferred from the gas storage tank to another pressure chamber. Of course, some or all of the CO₂ gas may be vented to atmosphere.

[0031] In some embodiments according to the present invention, the pressure chamber is depressurized such that, at the time the CO₂ gas is removed from the pressure chamber, the maximum density of a CO₂-containing composition in the pressure chamber is less than the critical density of the CO₂-containng composition. Preferably, the maximum density of the CO₂-containing composition in the pressure chamber is less than about 0.4 grams/cm³. More preferably, the maximum density of the CO₂-containing composition in the pressure chamber is between about 0.2 and 0.3 grams/cm³.

[0032] After depressurizing the pressure chamber, the substrate is removed from the pressure chamber (170). In some embodiments, the substrate is placed in another pressure chamber following removing the substrate from the pressure chamber. The process of removing the substrate from the pressure chamber and placing the substrate in another pressure chamber is preferably automated. After placing the substrate in the other pressure chamber, a subsequent process may be performed on the substrate in the other pressure chamber. The subsequent process may employ CO₂ as a processing fluid or may be a non-CO₂ based process. After placing the substrate in the other pressure chamber, the other pressure chamber may be pressurized using CO₂ gas from the pressure chamber as described above.

[0033] Methods according to embodiments of the present invention may have improved processing times when compared with processing times of for conventional processes that employ, for example, supercritical carbon dioxide as a processing fluid. Processes according to embodiments of the present invention have processing times that are preferably less than 2 minutes, more preferably less than 135, 90, or 75 seconds, and still more preferably less than 70, 60, 50 or 45 seconds.

[0034] Referring now to FIG. 2, an apparatus 200 according to embodiments of the present invention will now be described. As illustrated, the apparatus 200 is a cluster tool apparatus configured to perform chemical mechanical planarization processes on microelectronic device substrates. The apparatus 200 includes a transfer module 210. The transfer module is coupled to a first loadlock module 230 a and a second loadlock module 230 b. Although the embodiments illustrated in FIG. 2 show the transfer module coupled to first loadlock module 230 a and second loadlock module 230 b, it is to be understood that transfer modules according to embodiments of the present invention may be coupled to one or more loadlock modules. While the embodiments illustrated in FIG. 2 show the loadlock modules 230 a and 230 b coupled directly to the transfer module 210, it is to be understood that transfer modules of the present invention may be coupled indirectly (e.g., with an intervening transfer module) to the loadlock modules.

[0035] First and second loadlock modules 230 a and 230 b, respectively, each have a wafer cassette, 231 a and 231 b, respectively, that include one or more wafers 232. The wafer 232 is a wafer of semiconductor material such as silicon, silicon oxide, gallium arsenide, etc. Other types of workpieces may be cleaned or otherwise treated using the apparatus including, for example, various other semiconductor substrates as will be understood by those skilled in the art. The wafer 232 is in need of chemical mechanical planarization processing.

[0036] The transfer module 210 includes a robot 220. The robot 220 includes a base 222 coupled to the transfer module 210. The base 222 is coupled to a first extendable arm 226 a. The first extendable arm 226 a is coupled to a second extendable arm 226 b, which is coupled to a substrate engagement member 228. While the substrate engagement member 228 is preferably configured to transfer a single wafer, it is to be understood that substrate engagement members according to the present invention may be configured to transfer a cassette including one or more wafers. Although the transfer module 210 as illustrated in FIG. 2 includes a robot 220, it is to be understood that transfer modules of the present invention may include various other transfer mechanisms as will be understood by those skilled in the art.

[0037] As illustrated in FIG. 2, the transfer module 210 has a circular configuration. It is to be understood that transfer modules according to the present invention may have various other configurations including, but not limited to, track configurations as will be understood by those skilled in the art.

[0038] The transfer module 210 is coupled to a chemical mechanical planarization (CMP) module 233. The CMP module 210 may be various modules as will be understood by those skilled in the art. Preferably, the CMP module 210 employs a CO₂-based slurry and/or a CO₂-philic slurry as described in co-pending and co-owned application, Ser. No. 09/816,956 filed Mar. 23, 2001, which is incorporated herein by reference in its entirety.

[0039] The transfer module 210 is coupled to a rinse module 235 as will be understood by those skilled in the art. The rinse module 235 may employ various rinse fluids as will be understood by those skilled in the art. In a preferred embodiment, the rinse module 235 employs a CO₂-based fluid as a rinse fluid.

[0040] The transfer module 210 is further coupled to a liquid CO₂ cleaning module 237. The liquid CO₂ cleaning module 237 is capable of removing a waste layer comprising CMP residue and will be described further hereinbelow. While the embodiments illustrated in FIG. 2 show a separate liquid CO₂ cleaning module 237 and rinse module 235, it is to be understood that the rinse function and the liquid CO₂ cleaning function may be performed by the same module, particularly, but not exclusively, when the rinse fluid comprises liquid CO₂.

[0041] A control system 240 is coupled to the transfer module 210. The control system 210 is configured to control the transfer of the wafers from module to module, to control the conditions (e.g., pressure and temperature) of the various modules, etc. While the embodiments illustrated in FIG. 2 show an apparatus 200 having a single control system 210, it is to be understood that apparatus according to the present invention may have one or more control systems. For example, each module in the cluster tool could have its own control system.

[0042] While various processing fluids may be utilized in the various processing modules of the apparatus 200, it may be preferable to employ liquid CO₂ as the processing fluid in the CMP module 233, the rinse module 235 and the liquid CO₂ cleaning module 237. By employing liquid CO₂ in each of the processing modules, it may be possible to maintain the entire apparatus at a single operating pressure, rather than have to pressurize and depressurize each module to the modules required operating pressure. Maintaining the entire apparatus at a single operating pressure may improve the processing time for the apparatus by eliminating many of the pressurization/depressurization steps. Maintaining the entire apparatus at a single operating pressure for using liquid CO₂ may also provide a cleaner process because the apparatus will be operated at a positive pressure, rather than a vacuum.

[0043] Turning now to FIG. 3, a liquid CO₂ cleaning system 300 according to embodiments of the present invention for use with an apparatus such as the one described above with reference to FIG. 2 will now be described. The liquid CO₂ cleaning system 300 includes a pressure chamber 350 that preferably resides in a liquid CO₂ cleaning module, such as the liquid CO₂ cleaning module 237 described above with reference to FIG. 2. The pressure chamber 350 is configured to clean a microelectronic substrate as will be understood by those skilled in the art.

[0044] The pressure chamber 350 is in fluid communication with a liquid carbon dioxide supply system 360. The liquid carbon dioxide supply system 360 is configured to deliver liquid carbon dioxide or a liquid carbon dioxide based cleaning composition to the pressure chamber. The pressure chamber 350 is also in fluid communication with a liquid carbon dioxide collection system 370. The liquid carbon dioxide collection system 370 is configured to receive liquid carbon dioxide that is removed from the pressure chamber 350. The liquid carbon dioxide collection system 370 is in fluid communication with a liquid carbon dioxide rejuvenation system 390, which rejuvenation system is in fluid communication with the liquid carbon dioxide supply system 360. The liquid carbon dioxide rejuvenation system 390 is configured to remove contaminants from the liquid carbon dioxide in the liquid carbon dioxide collection system 370 such that the “rejuvenated” liquid carbon dioxide, which is preferably pure liquid carbon dioxide, can be introduced into the liquid carbon dioxide supply system 360. In this way, the rejuvenated liquid carbon dioxide may be re-used in the pressure chamber 350. While the embodiments illustrated in FIG. 3 show a liquid carbon dioxide collection system 370, it is to be understood that liquid CO₂ cleaning apparatus of the present invention need not have a liquid carbon dioxide collection system. Liquid CO₂ can be removed from the pressure chamber 350 in various other ways. For example, the liquid CO₂ can be removed by venting to atmosphere, by transferring to another pressurized pressure chamber, or by transferring directly to the liquid carbon dioxide rejuvenation system 390.

[0045] The pressure chamber 350 is also in fluid communication with a pressurized gas delivery system 380. The pressurized gas delivery system 380 is configured to introduce pressurized gas, such as CO₂ gas, non-CO₂ gas or a mixture thereof into the pressure chamber 350.

[0046] The pressure chamber 350 is further in fluid communication with an adjunct addition system 355. The adjunct addition system 355 is configured to deliver an adjunct to the pressure chamber 350. While the embodiments illustrated in FIG. 3 show an adjunct addition system 355 that is in direct fluid communication with the pressure chamber 350, it is to be understood that adjunct addition systems according to the present invention may be in fluid communication with the liquid carbon dioxide delivery system 360.

[0047] Referring now to FIG. 4, embodiments of the liquid CO₂ cleaning apparatus described in general with respect to FIG. 3 will now be described in more particularity. A pressure chamber 452 contains a microelectronic substrate 454. The pressure chamber 452 is in fluid communication with a liquid carbon dioxide supply vessel 462 via lines 463 and 466, valves 464 and 466 and a pump 465. The liquid carbon dioxide supply vessel 462 is capable of storing liquid carbon dioxide as will be understood by one skilled in the art. The pump 465 is capable of pumping liquid carbon dioxide as will be understood by one skilled in the art. An adjunct addition tank 456 is in fluid communication with the line 463 at the inlet to the pump 465 via a line 458 and a valve 457.

[0048] The pressure chamber 452 is in fluid communication with a liquid carbon dioxide collection vessel 471 via a line 473 and a valve 472. The line 473 is preferably a drain line. The vapor space of the pressure chamber 452 is in vapor communication with the vapor space of the liquid carbon dioxide collection vessel 471 via a line 478 and a valve 479. The liquid carbon dioxide collection vessel 471 is capable of storing liquid carbon dioxide as will be understood by one skilled in the art. The contents of the liquid carbon dioxide collection vessel 471 can be purged via lines 475 and 476 and valves 474 and 477.

[0049] Alternatively, the contents of the liquid carbon dioxide collection vessel 471 can be transferred to a still 491 via line 470 and valve 492. The still 491 is capable of distilling contaminated liquid carbon dioxide to remove the contaminants therefrom and provide pure carbon dioxide vapor. The still 491 is in fluid communication with a condenser 497 via a line 496 and a valve 495. The condenser 497 is capable of condensing the carbon dioxide vapor produced in the still 491 to provide pure liquid carbon dioxide to the liquid carbon dioxide supply vessel 462 via a line 499 and a valve 498.

[0050] A pressurized gas supply vessel 482 is in fluid communication with the pressure chamber 452 via a line 484 and a valve 486. The pressurized gas supply vessel 482 is capable of delivering a supply of pressurized CO₂ gas, supercritical CO₂, a non-CO₂ gas, or a mixture thereof as will be understood by those skilled in the art.

[0051] A vapor storage vessel 486 is in fluid communication with the vapor space of the pressure chamber 452 via a line 487 and a valve 488. The vapor storage vessel 486 is capable of withstanding system pressure and temperature as will be understood by those skilled in the art. In some embodiments, the vapor storage vessel 486 may be coupled to another pressure chamber. The other pressure chamber may be on the same apparatus as the pressure chamber 452, may be on a separate cluster tool apparatus, or may be on a separate non-cluster tool apparatus.

[0052] As will be understood by those skilled in the art, fluid transfer devices such as pumps and compressors may be inserted into one or more of the various lines as needed in order to facilitate fluid transfer. One who is skilled in the art will appreciate that lines may be selected from a group comprising piping, conduit, and other means of fluid communication that can withstand system temperature and pressure. One who is skilled in the art will also understand that a where one line has been shown in the given embodiment, multiple lines may be employed to provide, for example, supply and return piping. Additionally, more valves may reside in the one or more lines as appropriate.

[0053] While embodiments of the liquid CO₂ cleaning apparatus according to the present invention described in FIGS. 3 and 4 above have been illustrated for use as a liquid CO₂ cleaning module in embodiments of a CMP cluster tool described in FIG. 2 above, it is to be understood that liquid CO₂ cleaning modules according to the present invention that employ liquid CO₂ cleaning systems of the present invention may be used in various cluster tools (e.g., microelectronic substrate fabrication cluster tools) in conjunction with CO₂-based and non-CO₂-based modules as will be understood by those skilled in the art. For example, liquid CO₂ cleaning modules of the present invention may be used in cluster tools in conjunction with various processing modules including, but not limited to, etch modules; deposition modules such as pulsed vapor deposition modules, chemical vapor deposition modules, electroplating modules, dielectric layer deposition modules, and thin-film deposition modules; implantation modules such as ion implantation modules; chemical mechanical planarization modules; and photolithography modules such as photoresist application modules, photoresist exposure modules and photoresist development modules.

[0054] Preferably, liquid CO₂ cleaning modules of the present invention may be used to replace various conventional dry and/or wet cleaning modules that are currently used, for example, in conventional cluster tools for microelectronic substrate fabrication. Preferably, liquid CO₂ cleaning modules may replace conventional dry and/or wet cleaning modules that are used to remove various waste residues generated during microelectronic substrate fabrication including, but not limited to, chemical mechanical polishing residues, post-ion implantation residues, reactive ion etch residues, post-ash residues, and photoresists.

[0055] An example of a microelectronic substrate fabrication method that utilizes a liquid CO₂ cleaning module of the present invention will now be described. A substrate having a photoresist pattern thereon is placed into a first module such as a plasma etch chamber of a cluster tool and dual damascene structures such as vias or trenches are etched into low-k material. Next, the post-plasma etch substrate is placed in a second module, which is a plasma strip chamber used to remove photoresist from the substrate. The post-plasma strip substrate is then placed in a liquid CO₂ cleaning module of the present invention such as those described above. The liquid CO₂ cleaning module of the present invention is used to remove the reactive ion etch and remaining photoresist from the substrate. The liquid CO₂ cleaning module also preferably removes impurities and particles from surfaces of the substrate pre-metallization, which may, for example, improve contact resistance of an interconnect system. The liquid CO₂ cleaned substrate is then placed in a fourth module that is a barrier deposition module. After barrier deposition, the substrate is moved to a CVD Cu deposition module where metal is deposited onto the substrate. The post-metallization substrate is placed in a Cu CMP module, in which the Cu is planarized. The post-CMP substrate is then moved to a liquid CO₂ cleaning module according to the present invention for post-CMP cleaning to remove CMP residual impurities and particles from the substrate. While this process has been described using two separate liquid CO₂ cleaning modules, it is to be understood that this process could be performed using a single liquid CO₂ module that may employ different adjuncts to achieve the desired cleaning process.

[0056] Another example of a microelectronic substrate fabrication process that utilizes a liquid CO₂ cleaning module according to embodiments of the present invention will now be described. A substrate having a photoresist pattern thereon is placed into a first module that is a reactive ion etch (RIE) module. The post-RIE substrate is placed in an ion implantation module. The post-ion implantation substrate is placed in a liquid CO₂ cleaning module according to the present invention as described above. The liquid CO₂ cleaning module removes the ion implantation residue.

[0057] In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims. 

That which is claimed is:
 1. A method for cleaning a microelectronic substrate in a cluster tool comprising: placing the substrate in a pressure chamber of a module in the cluster tool; pressurizing the pressure chamber; introducing liquid CO₂ into the pressure chamber; cleaning the substrate in the pressure chamber; removing the liquid CO₂ from the pressure chamber; depressurizing the pressure chamber; and removing the substrate from the pressure chamber.
 2. The method according to claim 1, wherein the pressure chamber processing time is less than 2 minutes.
 3. The method according to claim 1, wherein the pressure chamber processing time is less than 90 seconds.
 4. The method according to claim 1, further comprising maintaining conditions in the pressure chamber at or below saturation conditions for the liquid CO₂ while removing the liquid CO₂ from the pressure chamber.
 5. The method according to claim 1, wherein greater than about 99 percent of the mass of the liquid CO₂ in the pressure chamber is removed from the pressure chamber as liquid CO₂.
 6. The method according to claim 1, further comprising maintaining the liquid CO₂ as subcooled liquid CO₂ while removing the liquid CO₂ from the pressure chamber.
 7. The method according to claim 1, wherein the flow rate of liquid CO₂ from the pressure chamber is greater than about 0.1 chamber volumes per second.
 8. The method according to claim 1, wherein the removing of the liquid CO₂ from the pressure chamber comprises: introducing a pressurized gas into the pressure chamber; and forced plug flowing the liquid CO₂ out of the pressure chamber.
 9. The method according to claim 8, wherein the pressurized gas comprises CO₂ gas.
 10. The method according to claim 9, wherein the pressurized gas is CO₂ gas that is at a pressure greater than the pressure in the pressure chamber and is at a temperature greater than the temperature in the pressure chamber.
 11. The method according to claim 8, wherein the pressurized gas comprises supercritical CO₂.
 12. The method according to claim 11, wherein the pressurized gas is supercritical CO₂ that is at a pressure greater than the pressure in the pressure chamber, is at a temperature greater than the temperature in the pressure chamber, and has a density less that the density of the liquid CO₂ in the pressure chamber.
 13. The method according to claim 8, wherein the pressurized gas comprises an inert gas.
 14. The method according to claim 1, wherein the introducing of the liquid CO₂ into the pressure chamber comprises partially filling the pressure chamber with liquid CO₂ such that a liquid volume and a vapor volume is formed.
 15. The method according to claim 14, wherein the removing of the liquid CO₂ from the pressure chamber comprises: providing fluid communication between the vapor volume of the pressure chamber and the vapor volume of a liquid CO₂ storage tank; and draining the liquid CO₂ from the pressure chamber to the liquid CO₂ storage tank.
 16. The method according to claim 1, wherein CO₂ gas remains in the pressure chamber after the removing of the liquid CO₂ from the pressure chamber.
 17. The method according to claim 16, wherein the depressurizing of the pressure chamber comprises removing the CO₂ gas from the pressure chamber.
 18. The method according to claim 17, further comprising storing the removed CO₂ gas in a gas storage tank.
 19. The method according to claim 18, further comprising charging the removed CO₂ gas from the gas storage tank into the pressure chamber during a subsequent processing cycle.
 20. The method according to claim 17, wherein the removing of the CO₂ gas from the pressure chamber comprises venting the CO₂ gas to atmosphere.
 21. The method according to claim 17, wherein the removing of the CO₂ gas from the pressure chamber comprises transferring the CO₂ gas to the pressure chamber of another module on the cluster tool.
 22. The method according to claim 17, wherein the depressurizing of the pressure chamber comprises depressurizing the pressure chamber such that, at the time the CO₂ gas is removed from the pressure chamber, the maximum density of a CO₂-containing composition in the pressure chamber is less than the critical density of the CO₂-containing composition.
 23. The method according to claim 22, wherein the maximum density of the CO₂-containing composition in the pressure chamber is less than about 0.4 grams/cm³.
 24. The method according to claim 22, wherein the maximum density of the CO₂-containing composition in the pressure chamber is between about 0.2 and 0.3 grams/cm³.
 25. The method according to claim 1, further comprising placing the substrate in another pressure chamber following removing the substrate from the pressure chamber.
 26. The method according to claim 25, wherein the removing of the substrate from the pressure chamber and the placing of the substrate in another pressure chamber is automated.
 27. The method according to claim 25, further comprising performing a subsequent process on the substrate in the other pressure chamber.
 28. The method according to claim 27, wherein the subsequent process does not utilize CO₂.
 29. The method according to claim 25, wherein CO₂ gas remains in the pressure chamber after the removing of the liquid CO₂ from the pressure chamber and the method further comprises: removing the CO₂ gas from the pressure chamber; and charging the CO₂ gas into the pressure chamber of another module on the cluster tool after placing the substrate in the other pressure chamber.
 30. The method according to claim 1, wherein the cleaning of the substrate comprises flowing the liquid CO₂ over the surface of the substrate.
 31. The method according to claim 1, wherein a waste layer is on the substrate, and wherein the cleaning of the substrate comprises removing the waste layer from the substrate.
 32. The method according to claim 31, wherein the waste layer comprises chemical mechanical polishing residue.
 33. The method according to claim 31, wherein the waste layer comprises post-ion implantation residue.
 34. The method according to claim 31, wherein the waste layer comprises reactive ion etch residue.
 35. The method according to claim 31, wherein the waste layer comprises photoresist.
 36. The method according to claim 1, wherein the introducing of the liquid CO₂ into the pressure chamber comprises: forming a pool of the liquid CO₂ in the pressure chamber; and forming a gas phase in the pressure chamber that contacts the liquid CO₂ pool and separates the liquid CO₂ pool from a portion of the pressure chamber wall.
 37. The method according to claim 36, wherein the gas phase comprises CO₂ gas.
 38. The method according to claim 36, wherein the gas phase comprises a non-CO₂ gas.
 39. The method according to claim 38, wherein the non-CO₂ gas is selected from the group consisting of nitrogen, helium, argon, air, and mixtures thereof.
 40. The method according to claim 38, wherein the non-CO₂ gas is an inert gas.
 41. The method according to claim 1, further comprising maintaining the temperature of the liquid CO₂ in the pressure chamber between about −57° C. and 31° C.
 42. The method according to claim 1, further comprising: maintaining the temperature of the liquid CO₂ at or near constant; and maintaining the partial-pressure of CO₂ in the pressure chamber at or below saturation pressure for the pure liquid CO₂ at the constant or near constant temperature.
 43. The method according to claim 1, further comprising introducing an adjunct into the pressure chamber.
 44. The method according to claim 43, wherein the introducing of the adjunct into the pressure chamber occurs before introducing the liquid CO₂ into the pressure chamber.
 45. The method according to claim 43, wherein the introducing of the adjunct into the pressure chamber occurs concurrently with the introducing of the liquid CO₂ into the pressure chamber.
 46. The method according to claim 43, wherein the adjunct and the liquid CO₂ are introduced into the pressure chamber as a mixture.
 47. The method according to claim 43, further comprising: forming a mixture of the liquid CO₂ and the adjunct; and decreasing the density of the liquid CO₂ in the pressure chamber to deposit the adjunct from the mixture on the substrate.
 48. The method according to claim 47, wherein the decreasing of the density of the liquid CO₂ comprises increasing the temperature of the liquid CO₂ in the pressure chamber.
 49. The method according to claim 47, wherein the decreasing of the density of the liquid CO₂ comprises decreasing the pressure of the pressure chamber.
 50. A method for cleaning a microelectronic substrate comprising: placing the substrate in a pressure chamber; pressurizing the pressure chamber; introducing CO₂ into the pressure chamber; cleaning the substrate in the pressure chamber; removing the CO₂ from the pressure chamber; depressurizing the pressure chamber; and removing the substrate from the pressure chamber, wherein the elapsed time between placing the substrate in the pressure chamber and removing the substrate from the pressure chamber is less than 2 minutes.
 51. The method according to claim 50, wherein the elapsed time is less than 90 seconds.
 52. The method according to claim 50, wherein the elapsed time is than 60 seconds.
 53. An apparatus for processing a microelectronic substrate comprising: a transfer module; a first processing module that employs liquid carbon dioxide as a cleaning fluid coupled to the transfer module; and a second processing module coupled to the transfer module; and a transfer mechanism coupled to the transfer module, the transfer mechanism configured to move the substrate between the first processing module and the second processing module.
 54. The apparatus according to claim 53, wherein the second processing module does not employ carbon dioxide as a process fluid.
 55. The apparatus according to claim 53, wherein the first processing module comprises: a pressure chamber; and a liquid carbon dioxide supply system in fluid communication with the pressure chamber.
 56. The apparatus according to claim 55, wherein the liquid carbon dioxide supply system comprises a liquid carbon dioxide supply vessel in fluid communication with the pressure chamber.
 57. The apparatus according to claim 55, wherein the first processing module further comprises a liquid carbon dioxide collection system in fluid communication with the pressure chamber.
 58. The apparatus according to claim 57, wherein the liquid carbon dioxide collection system comprises a liquid carbon dioxide storage vessel configured to collect contaminated liquid carbon dioxide from the pressure chamber in fluid communication with the pressure chamber.
 59. The apparatus according to claim 58, wherein the liquid carbon dioxide storage vessel comprises a heating element and is capable of distilling pure liquid carbon dioxide from contaminated liquid carbon dioxide solutions.
 60. The apparatus according to claim 59, wherein the liquid carbon dioxide collection system further comprises a condenser having a vapor inlet in fluid communication with the liquid carbon dioxide storage vessel and a liquid outlet in fluid communication with the liquid carbon dioxide supply system.
 61. The apparatus according to claim 58, wherein the pressure chamber is in vapor communication with the liquid carbon dioxide storage vessel and the pressure chamber is separately in liquid communication with the liquid carbon dioxide storage vessel.
 62. The apparatus according to claim 57, wherein the first processing module further comprises a liquid carbon dioxide rejuvenation system in fluid communication with the carbon dioxide collection system and in fluid communication with the carbon dioxide supply system.
 63. The apparatus according to claim 62, wherein the liquid carbon dioxide rejuvenation system comprises: a still in fluid communication with the liquid carbon dioxide storage vessel; and a condenser having a vapor inlet in fluid communication with the still and having a liquid outlet in fluid communication with the liquid carbon dioxide supply system.
 64. The apparatus according to claim 55, wherein the first processing module further comprises a vapor storage system in fluid communication with the pressure chamber.
 65. The apparatus according to claim 64, wherein the vapor storage system comprises a vapor storage tank in fluid communication with the pressure chamber.
 66. The apparatus according to claim 64, wherein the vapor storage system comprises: a compressor in fluid communication with the pressure chamber; and a vapor storage tank in fluid communication with the compressor.
 67. The apparatus according to claim 57, wherein the first processing module further comprises a pressurized gas delivery system in fluid communication with the pressure chamber.
 68. The apparatus according to claim 67, wherein the pressurized gas delivery system is configured to deliver pressurized carbon dioxide gas.
 69. The apparatus according to claim 67, wherein the pressurized gas delivery system is configured to deliver supercritical carbon dioxide.
 70. The apparatus according to claim 67, wherein the pressurized gas delivery system is configured to deliver pressurized inert gas.
 71. The apparatus according to claim 57, wherein the first processing module further comprises an adjunct addition system in fluid communication with the pressure chamber.
 72. The apparatus according to claim 71, wherein the adjunct addition system is in fluid communication with the pressure chamber via the liquid carbon dioxide supply system.
 73. The apparatus according to claim 71, wherein the adjunct addition system is directly in fluid communication with the pressure chamber.
 74. The apparatus according to claim 53, further comprising a third processing module that employs liquid carbon dioxide as a processing fluid coupled to the transfer module, wherein the transfer mechanism coupled to the transfer module is configured to move the substrate between the first processing module, the second processing module and the third processing module.
 75. The apparatus according to claim 74, wherein the first processing module comprises a pressure chamber, and wherein the third processing module comprises a pressure chamber in fluid communication with the pressure chamber of the first processing module.
 76. The apparatus according to claim 74, wherein the first processing module comprises a pressure chamber; wherein the third processing module comprises a pressure chamber; and wherein the apparatus further comprises a carbon dioxide vapor storage vessel that is in fluid communication with the pressure vessel of the first processing module and is in fluid communication with the pressure vessel of the third processing module.
 77. The apparatus according to claim 53, further comprising a loadlock module coupled to the transfer module.
 78. The apparatus according to claim 53, further comprising a first loadlock module and a second loadlock module.
 79. The apparatus according to claim 53, wherein the second processing module comprises a semiconductor processing module.
 80. The apparatus according to claim 79, wherein the semiconductor processing module is selected from the group consisting of an etch module, a pulsed vapor deposition module, a chemical vapor deposition module, an electroplating module, a chemical mechanical planarization module, and a thin-film deposition module.
 81. The apparatus according to claim 53, wherein the transfer mechanism comprises a robot.
 82. The apparatus according to claim 81, wherein the robot comprises an extendable arm and substrate engagement member.
 83. The apparatus according to claim 53, wherein the transfer mechanism has a circular configuration.
 84. The apparatus according to claim 53, wherein the transfer mechanism has a track configuration. 